(A) Field of the Invention
The present invention relates to a periodic poling structure and an electrode element and a method for preparing the same, and more particularly, to a periodic poling structure for quasi-phase matching (QPM) and an electrode element and a method for preparing the same.
(B) Description of the Related Art
The periodic poling structure, formed on a ferroelectric single crystal such as lithium niobate, may be widely used in the optical fields such as optical storage and optical measurement. There are several methods for preparing the periodic poling structure, such as proton-exchanging, the electron beam-scanning method and the electric voltage applying method, etc.
U.S. Pat. No. 6,002,515 discloses a method for manufacturing a polarization inversion part on a ferroelectric crystal substrate. The polarization inversion part is prepared by steps of applying a voltage in the polarization direction of the ferroelectric crystal substrate to form a polarization inversion part, conducting a heat treatment for reducing an internal electric field generated in the substrate by having applied the voltage, and then reinverting polarization in a part of the polarization inversion part by applying a reverse direction voltage against the voltage that was previously applied. In other words, the method for preparing a polarization inversion part disclosed in U.S. Pat. No. 6,002,515 requires performing the application of electric voltage twice.
U.S. Pat. No. 6,353,495 discloses a method for forming an optical waveguide element. The disclosed method forms a convex ridge portion having a concave portion on a ferroelectric single crystalline substrate, and a ferroelectric single crystalline film is then formed in the concave portion. A comb-shaped electrode and a uniform electrode are formed on a main surface of the ferroelectric single crystalline substrate, and electric voltage is applied to these two electrodes to form a ferroelectric domain-inverted structure in the film in the concave portion.
U.S. Pat. No. 6,836,354 discloses a method for producing an optical waveguide by irradiating a laser beam onto an oxide single crystal material. The laser beam is irradiated onto an oxide single crystal to form an optical waveguide portion defined by laser working faces, which are then subjected to a wet etching process using, for example, a strong alkaline solution.
U.S. Pat. No. 6,631,231 discloses a method for preparing an Optical waveguide element. A ridge-type optical waveguide is joined to a surface of a substrate via a joining layer made of an amorphous material. Two grooves are formed to shape an optical waveguide of a ridge type structure by using a dicing device or a laser-working device, and a machining-type dicing is preferred.